1. Field of the Invention
The present invention relates to a fuel cell cogeneration system.
2. Description of the Related Art
FIG. 16 is a block diagram showing a construction of the conventional fuel cell cogeneration system (see Japanese Laid-Open Patent Application Publication No. 2002-042841, page 3 to 6, FIG. 1).
Turning to FIG. 16, the fuel cell cogeneration system comprises a fuel cell 1 configured to generate an electric power using a fuel gas and an oxidizing gas, a fuel processor 2 configured to generate the fuel gas by subjecting a material to a steam reforming reaction and a shift reaction, a fuel-gas humidifier 5 configured to humidify the fuel gas to be supplied to the fuel cell 1, an air supply device 6 configured to supply air as the oxidizing gas to the fuel cell 1, and an oxidizing-gas humidifier 7 configured to humidify the air.
The fuel cell cogeneration system further comprises a cooling pipe 8 through which antifreezing fluid is sent to the fuel cell 1 to adjust a temperature of the fuel cell 1, a pump 9 configured to circulate cooling water, and a heat exchanger 12 configured to exchange heat generated in the fuel cell 1 with an external heat transfer medium (e.g., city water). With this construction, the external heat transfer medium which has exchanged heat with the fuel cell 1 flows in a direction and is stored in a heat utilization means 16 such as a tank that recovers heat from the fuel cell 1, and during start of the fuel cell 1, a heat transfer controller 17 flows the external heat transfer medium from the heat utilization means 16 to the fuel cell 1 in a reverse direction so that the heat recovered by the heat utilization means 16 is transferred to the fuel cell 1 through the heat exchanger 12.
Like the conventional fuel cell cogeneration system, the use of the hot water stored in the heat utilization means as the heat for heating the fuel cell 1 during start, is optimal in terms of reduction of the start time and energy use efficiency. However, since consumers typically consume hot water regardless of the amount of hot water remaining within the heat utilization means, the hot water may run out with use when the hot water stored in the heat utilization means is running short. Especially when the heat utilization means is not internally equipped with a backup hot water supply device for ensuring the hot water, consumers are incapable of consuming the hot water. This presents a serious inconvenience.